Interlocked generator circuit



Patented May 29, .1951

UNITED STATES PATENT OFFICE 2,555,038 INTERLOCKED GENERATOR CIRCUITEdward M. Jones, Cincinnati, Ohio, assignor to The Baldwin Company,Cincinnati, Ohio, a corporation of Ohio Application December 6, 1946,Serial No. 714,601

17 Claims. 1

My invention relates to generator circuits in which a master oscillatorcontrols the operation of a second generator which in turn controls theoperation of a third, and so on throughout a desired series, thegenerators all operating at harmonically related frequencies. While suchsystems have other uses, they are especially valliable in electricalmusical instruments. Reference may be made to Patents 2,230,429 in thenames of Kock and Jordan, and 2,233,948 in the name of Kock, whichpatents deal with musical instruments employing systems of interlockedgenerators.

In such instruments it is usual to arrange the generators for all notesof the same nomenclature in a system in which there is a masteroscillator for the note in a high register, and a plurality ofcontrolled, interlocked generators for notes octavely related to thefirst. Since there are twelve semi-tones in the equitempered scale,twelve of these systems are provided in the instrument. There are meansfor deriving signals or oscillations from each oscillator or generatorin the system, and these signals are transmitted through switchesconnected with playing keys to appropriate headers. The oscillationsproduced are of complex wave form, and the desired variety of voices isobtained by filtering and other means.

In some suggested systems the pulsations from a controlling generatorwere caused to stabilize and fix the frequency of oscillation of acontrolled generator at a harmonically related value. It has hithertobeen suggested also, that if instead, the controlled generators are madeto be non-self oscillating and are arranged to be triggered intodischarge by alternate pulsations of the controllinggenerators, a numberof advantages are obtained. Should any controlling generator fail, thecontrolled generator and all generators following it in' the system willbecome and remain inoperative, but will not generate incorrect anduncontrolled frequencies.

Accordingly, systems have been provided in which the master generator isa regenerative self oscillator, alternate pulsations'of which-trigger adischarge in the circuit or a controlled generator which is incapable ofself-oscillation. Alternate pulsations from the controlled generator inturn trigger a discharge in the circuit of the nextcontrolledgenerator,- and so on. A system of this type is taught in thefirst of the patents referred to above.

kprincipal object'of this invention is the ro= 2 vision of improvementsin systems of this general type.

It is an object of this invention to provide a system in which greaterstability is obtained.

It is an object of the invention to provide a new and advantageous wayof coupling the first controlled generator to the master oscillator.

It is an object of the invention to provide a new and advantageous wayof coupling interstage beyond the master oscillator, and in particular amode of inductive coupling.

It is an object of the invention to provide a new and highlyadvantageous means for interstage coupling.

In the attainment of these objects I secure, as further objects of theinvention, a substantial simplification of circuits and elimination ofparts, together with markedly increased ease and simplicity of assembly.

These and other objects of the invention which will be set forthhereinafter or will be apparent to one skilled in the art from thefollowing teachings, I attain by that construction and arrangement ofparts and in that mode of operation of which I shall now describe anexemplary embodiment. Reference is made to the accompanying drawingswherein:

Figure 1 is a circuit diagram of an exemplary generating systemembodying my invention.

Figure 2 is a perspective view of an inductive coupling means.

Figure 1 is illustrative of a system comprising a master oscillator andfive controlled generator stages. More or fewer may be employed; but theillustrated system is typical of those used in an electrical organ ofconventional range. The tubes indicated are electronic discharge tubesof double construction, i. e., two sets of elements in one envelope; butother types of tubes may be employed.

The master oscillator uses the first section of tube l, comprising athermionic cathode 2, grid 3 and plate 4. The cathode 2 is connected asshown to a grounded lead 5. Generally throughout this description Ishall use ground as a common return for circuits, and as a secondterminal for sources of electric potential. The plate 4 has in serieswith it a winding 6 of an iron-cored transforme'r l. A source ofpositive or B+ potential is connected to a header H, and the platecircuit derives its B+ voltage from this header through a leadcontaining a resistance [2, as will be more fully described hereinafter.

The other winding l3 of the transformer 1 forms a resonant circuit witha fixed capacity I4 and a variable capacity 15 which is used for tuningthe master oscillator to the desired frequency. The resonant circuit isconnected to the grid 3 through a capacity It and shunt resistance ll.

The circuit thus far described will be seen to be a regenerativeoscillator circuit. The terminal I8 on the resonant circuit is shown asconnected to ground. However, I may insert in this connection anotheroscillator which, operating at subaudio frequency, supplies a variablevoltage modifying the frequency of the master oscillator and giving thusa frequency tremolo not alone to the oscillations produced by the masteroscillator but also to the oscillations produced by the controlledgenerators in the system. For deriving a signal at the frequency of themaster oscillator a connection is provided between the 13+ end of thetransformer winding 6 and ground, containing therein in series thecapacity 5, the resistance 9 and the resistance [0, with the signal lead19 connected to the junction point of the resistances.

The second stage generator in my system uses the second half of tube 1.Its plate 29 is connected to the B+ header ll through one coil 2| of aniron-cored transformer 22. The other coil 23 of this transformer is inseries with the grid 24 and. with capacities 25 and 26 which are inseries with each other, and the latter of which is connected to theground lead 5. A resistance 21 is in shunt to these capacities.

Alead 28 connected intermediate the capacities 25 and 25, and bypassedto ground by a resistance 29, serves as a take-01f for the signal fromthe second stage generator.

The capacity 26 is large in value and serves to provide a low impedanceoutput for the signal circuit while delivering thereto a preferredsawtooth waveform of signal. (The resistance 29 provides a drainage pathfor any direct current component which might appear as the result ofleakage in the capacity 25.) Moreover the much smaller capacity 25 isthus able to control the conditions permitting discharge in the secondhalf of the tube without being influenced by output circuits.

It will be noted that the cathode 30 is not grounded but instead isconnected to a lead 3| which, by reason of a source of control voltageis maintained at a positive potential above 1 ground. This biases thecathode 39 positively and renders the second stage generator circuitnon-self-oscillatory.

The connection to the plate 4 of the master oscillator (which connectionincludes the resistor 12) is not made directly to the B+ header H, butrather, as shown, is made through the winding 2! of the transformer 22.Consequently plate circuit pulsations of the master oscillator producepulsations in winding 2|, and corresponding pulsations are producedinductively in the described circuit of grid 24 of the second stagegenerator.

A discharge will occur in the second half of the tube I when the gridpotential becomes sufiicient to permit a discharge in spite of the biasof the cathode 39. Thus, if capacity 25 and resistance 21 are chosen tohave a discharging time (to bring the grid to the desired potential)somewhat greater than a cycle of the frequency of the master oscillator,the grid 24 will be brought to the potential which permits dischargeonly upon the occurence of alternate pulses received from the masteroscillator. Hence, the frequency of pulsations produced by the secondstage generator will be half the frequency of the oscillations producedby the master oscillator.

The third stage generator utilizes the first half of tube 32, and isgenerally similar in circuit to the second stage generator. The grid 33is connected through the winding 34 of an iron-cored transformer 35 to anetwork comprising capacities 36 and 37 and resistances 33 and 39, withprovision for a signal take-off at 40. The plate is connected throughthe other winding 42 of the transformer to the 13+ header H. The cathode43 is connected to the lead 3| and is therefore biased, so that thecircuit is non-self-oscillatory.

The remaining stages are similar to the third. In Figure 1, the secondhalf of the tube 32 is used for a fourth stage generator. Thetransformer for this stage is indicated at 44, with windings 45 and 46.The stage has a network of capacity and resistance including capacities4i and 48, resistances 49 and 59, with a signal take 01? at 5|.

The first half of the tube 52 is used for a fifth stage generator havinga transformer 53 with windings 54 and 55, a network comprisingcapacities 56 and 51, resistances 58 and 59 and a signal take off 60.

The second half of the tube 52 is used for a sixth stage generatorhaving a transformer 6| with windings 62 and 63, a network comprisingcapacities 64 and 55, resistors 66 and 61, with a signal take off at 68.

It will be understood that the cathodes of the several tubes are heatedby filaments powered from a suitable source of current (not shown).Twelve generating systems of the type described will take care of arange of six octaves in a musical instrument. In some instruments it isdesired to have one or more additional notes. Thus in a currentinstrument I provide a low 0 coupled to the last or sixth stage of aC-generator system of the kind illustrated. In this event it isadvantageous to interconnect the plate windings and 62 of transformers53 and GI by a resistance 69. Coupling between the sixth stage of theillustrated generator system and a suboctave generator may be elfectedthrough a lead to the point of connection of this resistance withwinding 62. Such a connection tends to drain away voltage and diminishthe strength of pulses received by the sixth stage from the fifth stagegenerator. The resistance 59 tends to compensate for this by providingelectrical in addition to magnetic transfer between the fifth and sixthstage. In a generator system in which the sixth generator is notrequired to control a suboctave generator the resistance 59 is omitted.

I have also shown a connection between the plate and cathode of the lasthalf of tube 52, which connection includes a capacity 10. Difficulty issometimes encountered due to the migration of electrons from one set oftube elements to another when employing double tubes as shown. Thecapacity 19, connected as shown, prevents incorrect discharge in thesecond half of the tube. I have not, however, found it necessary toprovide any such capacitative connection for any of the stages of mygenerator systems excepting the last.

The coupling between the second and following stages in the illustratedsystem is effected inductively, i. e. there is inductive couplingbetween transformers 22 and 35, and between the latter and transformer44, and so on throughout the system. This inductive coupling betweenstages I find provides greater stability of operation as compared withother systems of the type wherein interstage energy transfers areeffected electrically through capacities and/or resistances. The severaltransformers 22, 44, 53 and 6! may be made up as windings on single-legcores, and may be so mounted on a panel or the like that thetransformers are located close to each other in a series in which thecore legs are parallel. In this event the magnetic flux from atransformer, passing through the air, will affect the core of anadjacent transformer.

I prefer, however, to locate the windings for transformers 22, 35, 44,53 and SI on a single core as shown in Figure 2. Here the core II is soconstructed as to provide a closed magnetic circuit about all windings.Each of the winding assemblies 22a, 35a, 44a, 48a and 5Ia is locatedupon its own core leg 12, 13, l4, l5, and 16 forming part of the generalcore, and between the several winding assemblies I provide other corelegs 11, 18, 19, and 80.

A much closer magnetic coupling is obtained in this way, and one whichis not affected by external conditions. The legs 'l'i80 between windingsare in effect magnetic by-passes, and

offer a means of controlling the degree of magnetic coupling with greataccuracy. This is advantageous because the pulses received by acontrolled generator from a controlling generator should be strong, andare of fairly critical voltage value. Control may easily be effected byapportioning the size of the by-pass core legs.

The structure shown in Figure 2 has other advantages. It is a lessexpensive structure when the several windings are placed on the samecore rather than on separate cores. The structure provides a single unitwhich may be mounted in any convenient place in a generator system. Thelocation of individual transformers on a panel or the like, andadjustment of their respective positions to secure proper magnetic orinductive coupling is not involved.

The inductive coupling which I have described results in thetransference of pulses from a controlling generator to a controlledgenerator as will now be understood. The third stage generator receivespulses from the second stage generator through its transformer 35. Thesepulses momentarily reduce the negative potential of the grid 33, and adischarge will occur in the first half of the tube 32 if the capacity 35has diucharged through the resistance 38 enough to permit the grid 33 tocome to a sufliciently small negative potential with respect to thecathode 43, positively biased as previously described. The capacity 36recharges upon the occurrence of discharge in the tube, terminating thedischarge and bringing the grid to a sufliciently negative potentialsuch that a pulse from the second stage generator will not again cause adischarge in the third stage until the capacity 36 has again dischargedsufficiently through resistance 33. A similar action occurs in thefourth stage generator, the coupling being between transformers 35 .and44, and so on throughout the series.

The tuning throughout the several controlled generators in a system willvary; but this can largely be accomplished by Variations in the sizes ofthe parts indicated. Furthermore, a structure like that shown in Figure2 may be made as a standard item, and used for all of the generatorsystems in an electrical musical instrument, with appropriate changes inthe values of the other circuit elements. This further makes forsimplicity and economy.

The values of the circuit elements in a gen- Iii) erator system may bechosen by the skilled. worker in the art in the light of these teachingsto give him a system which will produce the desired harmonically relatedfrequencies. By way of example, I give the following as constants andparts in an exemplary system or series, this being the one for theproduction of the o'ctavely related A notes of a musical instrument:

Signal frequencies At I9, 1760 cycles per second At 28, 880 cycles persecond At 40, 440 cycles per second At 5|, 220 cycles per second At 60,110 cycles per second At 68, 55 cycles per second Resistances 9, 47,000ohms 49, 85,000 ohms l0, 1,800 ohms 50, 4,700 ohms [1, 270,000 ohms 58,85,000 ohms- 21, 85,000 ohms 59, 4,700 ohms 29, 4,700 ohms 65, 80,000ohms 38, 55,000 ohms 61, 4,700 ohms 39, 2,200 ohms 69, 700,000 ohmsCapacities 8, .02 microfarad 31, .2 microfarad I4, .0011 microfarad 41,.025 microfarad i5, .0003.0006 48, .25 microfarad microfarad 56, .05microfarad I6, .002 microfarad 51, .5 microfarad 25, .006 microfarad 64,.1 microfarad 26, .06 microfarad 65, 1.0 microfarad 36, .02 microfarad70, .0003 microfarad Tubes Type 6SN7 Potentials At II, 165 volts At 3!,15 volts Master oscillator transformer Winding l3, 5 henries Winding 6,approx. .14 henry (Turns ratio 6:1)

Interstage coupling Winding Zl 480 turns core leg I2 width Winding 23240 turns core leg ll 3%" width Winding 34 240 turns core leg 13 widthWinding 42 480 turns core leg 18 A1" width Winding 45 680 turns core leg14 width Winding 46 340 turns core leg 19 width Winding 54 480 turnscore leg 15 width Winding 55 960 turns core leg 80 width Winding 62 960turns core leg width Winding 63 480 turns Window areas for windings:each 1%;" x A; core material and thickness: 32 laminations, interleavedEs and Is, .014", Allegheny Ludlum Steel Corporation Audio A.

Modifications may be made in my invention Without departing from thespirit of it. Having thus described my invention in an exemplaryembodiment, what I claim as new and desire to secure by Letters Patentis:

1. In a generator system, a generator comprising a thermionic tubehaving a plate, a grid and a cathode, a transformer having a pair ofwindings, one of said windings being connected between said plate and asource of positive potential, the other of said windings being in serieswith said grid in a grid-to-cathode circuit containing a capacity and agradual discharge shunt,

said cathode being connected to a source of positive potential so as tobias said cathode to prevent said generator from producingself-oscillations without external excitation, and magnetic means injuxtaposition to one of said windings for impressing upon said windingmagnetic pulses from an outside source to create correspondingelectrical pulses in said winding for biasing the said grid sufficientlyto overcome the bias of said cathode upon sufiicient discharge of saidcapacity, to permit discharges to occur in said tube.

2. The structure claimed in claim 1 wherein said magnetic meansimpresses pulses on said winding of a desired frequency, and wherein thevalue of said capacity is such as to have a period of discharge to bringsaid grid to operative potential, which period of discharge is greaterthan a cycle of said frequency whereby discharges are caused to occur insaid tube at a frequency harmonically related to said first mentionedfrequency and not greater than one-half thereof.

3. The structure claimed in claim 1 wherein said magnetic meansimpresses pulses onsaid winding of a desired frequency, and wherein thevalue of said capacity is such as to have a period of discharge to bringsaid grid to operative potential which period of discharge is greaterthan a cycle of said frequency, whereby discharges are caused to occurin said tube at a frequency harmonically related to said first mentionedfrequency and not greater than onehalf thereof, and in which the saidcircuit from the grid to cathode includes means to derive a signaltherefrom at the second mentioned frequency.

4. In a generator system, a generator comprising a thermionic tubehaving a plate, a grid and a cathode, a transformer having a pair ofwindings, one of said windings being connected between said plate and asource of positive potential, the other of said windings being in serieswith said grid in a grid-to-cathode circuit containing a capacity and agradual discharge shunt, said cathode being connected to a source ofpositive potential so as to bias said cathode to prevent said generatorfrom producing self-oscillations without external excitation, and meansfor impressing upon said generator pulses from an outside source to biasthe said grid sufiiciently to overcome the bias of said cathode uponsufiicient discharge of said capacity, to permit a discharge to occur insaid tube, in combination with a second generator comprising a plate, agrid and a cathode, a transformer having a pair of windings, one of saidwindings being connected between said plate and a source of positivepotential, the other of said windings being in series with the grid ofsaid second generator in a grid-to-cathode circuit containing a capacityand a gradual discharge shunt, said cathode of said second generatorbeing connected to a source of positive potential so as to bias saidlast mentioned cathode to prevent said second generator from producingself-oscillations without external excitation, the transformers of thetwo generators being so related to each other that an inductive couplingoccurs between them whereby a discharge occurring in the first mentionedgenerator will produce a pulse in the circuits of the second generatortending to bring the grid of said second genera tor toward a potentialpermitting discharge be tween the cathode and plate thereof.

5. The structure claimed in claim 4 in which the first generatorproduces successive pulses of r cillations produced by a desiredfrequency, and in which the capacity in the grid-to-cathode circuit ofthe second generator has a period of discharge to bring the grid thereofto a potential for discharge greater than a cycle of the frequency ofthe first generator, so that discharges occur in the second generator atan harmonically related frequency not greater than one-half thefrequency of the first generator.

6. In a generator system, a master oscillator comprising a thermionictube having a plate, a grid and a cathode, said elements having circuitsrelated for self-oscillation at a desired frequency, a second generatorcom rising a plate, a grid and a cathode, a transformer having windings,one of said windings being in a circuit between said plate and a sourceof positive potential, the other of said windings being in series withsaid grid in a grid-to-cathode circuit, the plate of said nasteroscillator being connected to a source of positive potential through theplate winding of the transformer of the said second generator, wherebyoscillations produced by said master oscillator produce pulsations inthe circuits of said second generator, and means for biasing said secondgenerator to prevent self-oscillation so that a discharge between thecathode and plate of said second generator can occur only upon theoccurrence of a pulse from said master oscillator.

7. In a generator system, a master oscillator comprising a thermionictube having a plate, a grid and a cathode, said elements having circuitsrelated for self-oscillation at a desired frequency, a second generatorcomprising a plate, a grid and a cathode, a transformer having windings,one of said windings being in a circuit between said plate and source ofpositive potential, the other of said windings being in series with saidgrid in a grid-to-cathode circuit, the plate of said master oscillatorbeing connected to a source of positive potential through the platewinding of the transformer of the second mentioned generator, wherebyossaid master oscillator produce pulsations in the circuits of saidsecond generator, and means for biasing said second generator to preventself-oscillation so that a discharge between the cathode and plate ofsaid second generator can occur only upon the occurrence of a pulse fromsaid master oscillator, the means for biasing said second generatorcomprising means for maintaining the cathode thereof at a positivepotential, the said grid circuit of said second generator containing acapacity with discharging means and having a period of discharge to biasthe grid thereof to permit a discharge between the corresponding cathodeand plate at a period more than the period of a cycle of the frequencyof the master oscillator, so that a discharge occurs in the secondgenerator at an harmonically related frequency not greater than one-halfthe frequency of the master oscillator.

8. In a generating system, a source of oscillations and a series ofcontrolled generators, each of said controlled generators comprising athermionic tube having a plate, a grid and a cathode, a transformerhaving windings, a plate-tocathode circuit containing one of saidwindings in series and connecting said plate to a source of positivepotential, a grid-to-cathode circuit containing the other of saidwindings in series therewith, means for transferring pulses from saidsource to the first of said generators to produce discharges in thegenerator bearing an harmonic relation to said pulses, the transformersof the several controlled generators being inductively coupled one toanother in a series whereby pulses occurring upon discharge in the firstgenerator are transmitted to the circuits ofQthe second generator and soon, said controlled generators having their respective cathodes biasedto a positive potential preventing self-oscillation, the respectivegrid-to-ca/thode circuits of the controlled generators containingcapacities which, become charged upon discharge of the tube, and whichupon discharge permit the respective grids of said generators to bebrought toward potentials permitting discharge under the influence ofincoming pulses. 9. The structure claimed in claim 8 wherein each suchcapacity has a discharging period to bring its grid to the potential fordischarge, which period is greater than a cycle of the frequency ofpulsations impressed upon it by a preceding source or generator so thatdischarges occur in a controlled generator at a frequency harmonicallyrelated to but not greater than one-half the frequency of the pulsesimpressed thereon.

1,10. The structure claimed in claim 8 wherein each such capacity has adischarging period to bring its grid to the potential for discharge,which period is greater than a cycle of the frequency of pulsationsimpressed upon it by a preceding source or generator so that dischargesdcfcur in a controlled generator at a frequency harmonically related tobut not greater than one-half the frequency of the pulses impressedthereon, and in which each controlled generator has means for deriving asignal therefrom.

11. In a series of serially controlled generatdrs, each generator havinga thermionic tube with a plate, a grid and a cathode and each controlledgenerator having a transformer with windings located respectively inplate and grid circuits thereof, a structure comprising a com-- monmagnetic core, the windings of the transformers of a plurality of thecontrolled generators being located on said core, said core providing aclosed magnetic path about all windings, a separate leg for eachtransformer and legs between transformers serving as magnetic by'-passesto control the degree of coupling between transformers.

-.{ 12. The structure claimed in claim 11 wherein 13. In a generatorseries comprising a master oscillator and a plurality of controlledgenerators, each involving a thermionic tube having a plate, a grid anda cathode, and each controlled generator having a transformer comprisingprimary and secondary windings, a common structure comprising a core ofmagnetic material with separate legs for each of said transformers, andmeans providing legs forming magnetic bypasses located betweentransformers whereby to provide controlled inductive coupling betweensaid several transformers successively.

14. In a system for producing harmonically related electric pulses, thecombination of at least two pulse generators in a series, each of saidgenerators including a thermionic tube having a plate, a grid and acathode, a transformer having windings, a plate-to-cathode circuitcontaining one of said windings, and a grid-tocathode circuit containinganother of said windings, the transformers of the two adjacentgenerators being in juxtaposition on a common magnetic core so as to bemagnetically coupled, said core having magnetic bypass means between thesaid transformers whereby pulses in one generator initiate fractionalharmonically related pulses in an adjacent generator without thenecessity of conductive coupling therebetween.

15. The structure claimed in claim 8 wherein said transformer has a coreproviding a closed magnetic path about all windings, a separate leg foreach pair of windings and legs between said pairs of windings serving asmagnetic bypasses to control the degree of coupling between said pairsof windings.

16. The structure claimed in claim 11 wherein said core is composed ofinterleaved E and I laminations.

1'7. The structure claimed in claim 13 wherein said core is composed ofinterleaved E and I laminations.

EDWARD M. JONES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,980,911 Coupleux Nov. 13, 19342,301,869 Hammond Nov. 10, 1942 2,328,282 Kock Aug. 31, 1943

